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ABSTRACT-In the Gila River drainage of southwestern New Mexico, roundtail chub (Gila robusta) were historically widespread and relatively common in mainstream and larger tributary habitats. Natural and human-induced habitat alterations and establishment of non-native predator fishes are believed to be the primary reasons for the current reduced range and abundance of this species. Roundtail chub has been extirpated from the San Francisco River, a major tributary of the Gila River. It persists mainly in reaches of the Gila River drainage that are free of non-native predators or where natural flow regimes and periodic flooding might act to suppress introduced predator populations and maintain habitat variability....
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The Iowa darter (Etheostoma exile) was first captured in Little Yampa Canyon, Yampa River, Colorado, by electrofishing in autumn 2003, and abundance of this nonnative species increased during 2004?2007. The Iowa darter also expanded downstream 229 river km, based on captures of young fish in a drift net at the confluence of the Yampa and Green rivers in 2005, and in light traps in the Green River near Jensen, Utah, in 2005?2007. Likely introduction of the Iowa darter via bait-bucket transfer suggests that additional legal deterrents might be needed to reduce further illicit introductions of potentially problematic nonnative fishes in the Colorado River Basin. Published in The Southwestern Naturalist, volume 53,...
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Predation experiments, field studies, and individual-based-model (IBM) simulations revealed factors that affected the survival and recruitment of early life stages of endangered Colorado pikeminnow Ptychocheilus lucius in the Green River basin, Utah and Colorado. Small-bodied, nonnative red shiners Cyprinella lutrensis attacked Colorado pikeminnow larvae an average of once per minute, and predation success approached 30% in laboratory aquaria. Attack rate was also high in mesocosm experiments; turbidity and alternative prey reduced predation success. Distributions of hatching dates derived from otolith daily increment analysis showed that large cohorts of Colorado pikeminnow larvae that hatched in the Green River...
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Historically widespread and abundant throughout warm water reaches of the Colorado River basin, the endemic razorback sucker (Xyrauchen texanus) is now rare and listed as endangered (United States Fish and Wildlife Service, 1991). Mainstem dams that alter habitat and introduction of non-native fishes which prey upon or compete with early life stages are among the large-scale ecological disturbances that have negatively affected the razorback sucker (Tyus, 1987; Minckley et al., 1991). Rarity of larval and especially juvenile razorback suckers in collections, and presence of only aged adults in remaining populations indicates recruitment failure (McCarthy and Minkley, 1987; Lanigan and Tyus, 1989; Minckley et al.,...
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The endangered bonytail Gila elegans, a large-bodied, main-stem cyprinid endemic to the Colorado River Basin of the American Southwest, was once widespread and abundant in warm-water-stream reaches. Negative effects of altered flow and temperature regimes downstream of dams, other habitat changes, and establishment of nonnative fishes have reduced populations of native fish throughout the basin, and wild bonytails may be extirpated. Hatchery reared bonytails are stocked in formerly occupied habitat to rebuild depleted populations, but their ecology is poorly understood. In 2002?2007, sampling in the middle Green River from upstream and downstream of stocking locations in Dinosaur National Monument documented survival...
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